в) $$n + \frac{5}{14} n = \frac{1}{7}$$
$$\frac{14}{14} n + \frac{5}{14} n = \frac{1}{7}$$
$$\frac{19}{14} n = \frac{1}{7}$$
$$n = \frac{1}{7} : \frac{19}{14}$$
$$n = \frac{1}{7} \cdot \frac{14}{19}$$
$$n = \frac{2}{19}$$
Ответ: $$n = \frac{2}{19}$$